1. Field of Invention
This invention improves control of the single pressure absorption refrigeration process, specifically it controls the cooling unit heat source when circulation of the refrigerant ceases.
2. Objectives and Advantages
Many applications use the single pressure absorption refrigeration (SPAR) system where portability is desired. The SPAR system does not have a mechanical pump whereas the dual pressure absorption system utilizes a mechanical pump. See Patent Application Pub. No. US 2005/0126192 for an example of a dual pressure absorption system. Mechanical pumps require an energy source therefore SPAR systems are ideal for applications where municipal power is not available. A few applications for the SPAR system are stand alone portable freezers and refrigerators, boats, recreational vehicles (RVs) and other transportation devices which require refrigeration storage. In addition to portable applications, the SPAR system is used in remote stationary applications. It came to the inventor's attention that the SPAR system will be destroyed by prolonged periods of operation when the absorption cycle has ceased.
The SPAR system requires an energy source to drive the absorption cycle. The energy source typically comes in the form of heat input to the cooling unit. The cooling unit is the assembly containing the absorption cycle. The energy or heat driving the absorption cycle is calibrated for a continuous cycle. When the absorption cycle ceases, continued heat input to the cooling unit results in system destruction. One form of system destruction is the thermo stresses introduced into the cooling unit tubing. Cracking and rupturing of the cooling unit tubing may result from repeated application of excessive thermo stresses. Under certain conditions, a cooling unit tubing rupture may result in a dangerous fire. Another form of system destruction can occur when the inhibitor is concentrated and crystallized. Finally, refrigeration stops when the absorption cycle ceases therefore energy is wasted.
When the SPAR is stationary, the cooling unit must be leveled according to the manufactures instructions/operator's manual in order to operate in a continuous cycle. In a vehicle application, typically the manufactures' operation manual states that the SPAR may be operated while in transit. The motion of transit prevents the refrigerant from pooling, where pooling is the primary cause of refrigerant cessation. During phases of transportation, such as brief rest stops, it is not always practical or convenient to level the system. One operator's manual states that if the vehicle is parked for several hours, and the refrigerator is operating, the vehicle should be leveled. The inventor destroyed a refrigerator by this method of operation assuming that less than two hours of operation off-level would not damage the system. This event led to the recognition by the inventor that an improved cooling unit heat source controller was needed.
In the stationary refrigeration application, it is desirable to reduce the amount of refrigerant in the system thereby making the system more efficient. See. U.S. Pat. No. 6,655,171 to Korinth (2003). An improved heat source controller which maintains tighter temperature and pressure limits preventing cessation of the refrigerant would benefit the system found in U.S. Pat. No. 6,655,171.
The inventor recognized that a control system would prevent the premature failure, possible fire hazard, and maintain cooling unit performance of a SPAR system by monitoring the cooling unit parameters and taking appropriate action when cessation of the refrigerant occurred. This led to the research and development of the absorption refrigeration protective controller (hereafter ARP controller).
3. Brief Discussion of Prior-Art
After performing a market, technical document, and patent search, no commercial devices or technical documents directly address the cessation of refrigerant problem or offered any obvious control solutions. U.S. Pat. No. 7,050,888 to Schneider et al. (2006) teaches that the: claimed device saves energy, but the device does not address system destruction by off-level operation. The only other prior-art found was a thermo-fuse which attempts to prevent fires due to overheating of the boiler casing. The thermo-fuse did not offer a solution for off-level operation system destruction. Rather, the thermo-fuse appeared to protect electrical equipment and not the SPAR cooling unit. Further discussion of prior-art, including test data, may be found in the Detailed Description sections below.